Arrangement in fuel injection apparatus

ABSTRACT

An arrangement in a fuel injection system for controlling the fuel injection includes a body part having a space, through which the fuel to be injected during operation flows, and a fuel inlet opening and an outlet opening opening into the space. A piston is arranged movably inside the space, the piston having a channel arranged therein for creating a flow connection between the fuel inlet opening and the outlet opening, whereby the piston divides the space into a first part connected with the inlet opening and a second part connected with the outlet opening. A spring creates a force acting on the piston in a direction opposite to that of the main fuel flow. The piston and the body part are formed so that when the piston is in the end adjacent the fuel inlet opening it delimits a third space, the volume of which depends on the mutual positions of the piston and the body part.

This is a national stage application filed under 35 U.S.C 371 based onInternational Application No. PCT/FI2004/000006 filed Jan. 9, 2004, andclaims priority under 35 U.S.C 119 of Finnish Patent Application No.20030054 filed Jan. 15, 2003.

BACKGROUND OF THE INVENTION

The present invention relates to an arrangement in a fuel injectionapparatus.

Common rail injection systems utilizing pressure accumulators arecurrently commonly used in connection with piston engines. In suchsystems the fuel stored in injection pressure in the so-called pressureaccumulator is injected into the combustion chamber of the engine bycontrolling the injector valve.

Generally, a flow fuse is used as a safety means in injection systems.The flow fuse is usually arranged between the pressure accumulator andthe injection valve. The flow fuse closes the flow path from theaccumulator in case of a leak and in case the injection valve is stuck,for example, in the open position, in which case there's a situationwhen fuel can uncontrollably leak into the cylinder combustion chamber.To avoid this situation, U.S. Pat. No. 3,780,716 and WO 95/17594disclose a flow fuse restricting the fuel flow volume. Typically theflow fuse includes a cylinder space that further includes a pistonapparatus having a spring load acting against the fuel flow directionduring injection. During normal action the fuel volume needed for eachinjection corresponds with the volume displaced by the piston. If, forsome reason, the injection valve starts to leak, the piston will move toits other limit position, where it will close the flow.

In a typical common rail system the injection pressure reaches a highpressure level almost instantaneously when the needle of the injectornozzle opens. As a result of this, the fuel mass flow is great right atthe beginning of the injection during injection of fuel into thecombustion chamber. In such a case the pressure in the combustionchamber can increase too fast for reaching optimum performance.

An aim of the present invention is to produce an arrangement in the fuelinjection apparatus minimizing the problems associated with prior art.It is an especial aim of the invention to produce an arrangement forrestricting the fuel mass flow in the beginning of the injection phase.

SUMMARY OF THE INVENTION

According to the invention, an arrangement in the fuel injection systemfor controlling the fuel injection comprises a body part with a spacearranged therein, through which space the fuel to be injected flowsduring operation, the space further having an inlet and an outletopening therein. The arrangement further comprises a piston means,arranged movably in the space and having a channel or the like forcreating a flow connection between the fuel inlet and the fuel outletopenings. In this arrangement the piston means can divide the space intothe first part, being in connection with the inlet opening, and thesecond part, being in connection with the outlet opening. Thearrangement further comprises a spring or the like for creating a forceacting on the piston means in a direction opposite to the main directionof fuel flow. The main characterizing feature of the arrangement is thatas the piston means is in the end adjacent the inlet opening or near it,the piston means and the body part delimit at least one third part ofthe space, the volume of which is dependent on the mutual positions ofthe piston means and the body part.

Preferably the piston means and the space are cylindrically formed andtogether they form at least two separate sliding surfaces, formed atdifferent distances in relation to the central axis of the piston meansand the space. In the arrangement, the third part of the space and itscondition can be defined by means of these sliding surfaces in apreferred way. In the arrangement, when the piston means is in the endadjacent the inlet opening, the volume of the third part of the space isat its smallest, and as the piston means retracts to a certain distancefrom the end adjacent the inlet opening, the volume of the third spaceincreases and as the piston means retracts beyond the said certaindistance, the third and the first parts of the space are combined. Thethird space part is in continuous flow connection with the fuel inletopening and/or the first space part. The flow connection is achieved bymeans of a throttling channel or the like.

The space is preferably cylindrical and it comprises at least twoportions having a different diameter, of which portions the one havingthe smaller diameter is located at the end adjacent the inlet opening.The piston means correspondingly includes two portions having differentdiameters, with the portion having the smaller diameter being located inthe end adjacent the inlet opening and both the longitudinal length ofthe section of the piston means having the smaller diameter and thelongitudinal length of the portion of the space having the smallerdiameter are shorter than the length of the stroke of the piston means.

As the piston means is located in the end adjacent the outlet opening,the piston means joins to the body part so as to close the flow path tothe inlet opening. Because of this, the arrangement according to theinvention also functions as a so-called flow fuse.

The arrangement according to the invention allows limiting the mass flowof the fuel injected in the beginning of the injection while allowing asufficient injection pressure during the actual injection. Further, thearrangement according to the invention also preferably produces a fuelflow fuse.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following the invention is described by way of example and withreference to the appended schematic drawings, of which

FIG. 1 shows the arrangement according to the invention being applied tothe fuel injection system of an engine;

FIG. 2 shows an embodiment of the arrangement according to theinvention;

FIG. 3 is section A—A of FIG. 2.

FIG. 4 shows the arrangement of FIG. 2 in a first extreme situation;

FIG. 5 shows the arrangement of FIG. 2 in an intermediate situation;

FIG. 6 shows the arrangement of FIG. 2 in another intermediatesituation;

FIG. 7 shows the arrangement of FIG. 2 in another extreme situation, and

FIGS. 8–10 show various embodiments of the arrangement of FIG. 2.

DETAILED DESCRIPTION

FIG. 1 shows very schematically, how the arrangement 4 according to theinvention can be arranged in connection with a common rail fuelinjection system of an internal combustion engine. Such a fuel injectionsystem is known as such, and it is described here only as far as isessential for understanding the operation of the invention. The fuelinjection system based on a common rail comprises as its main componentsthe common rail, i.e. pressure accumulator 1, in which fuel is stored inhigh pressure to be injected into the engine and which the injectionvalve 2 is in flow connection. A fuel channel system 3, 3′ has beenarranged between the common rail 1 to injection valve 2 metering thefuel to each cylinder (not shown) During operation, a sufficientpressure is maintained in the common rail achieving sufficient injectionpressure for the injection valve 2. Each injection valve 2 comprisescontrol means (not shown) for independently controlling the injection.Arrangement 4, the operation of which is described with reference toFIGS. 2–8, has been provided in the fuel channel system 3, 3′.

FIG. 2 shows the arrangement according to the invention in the positiontaken during injection and FIG. 3 shows the section A—A of FIG. 2.Arrangement 4 comprises a body part 5 with a cylindrical space 6 forfuel arranged therein. The fuel inlet opening 7 and the outlet opening 8have also been arranged in the body part 5, in connection with the fuelspace. The space 6 is also provided with a piston means 9. The pistonmeans comprises a channel or the like, such as the combination of bore12, 14 and the plane surface 15 of the piston means, the combinationallowing fuel to flow from the inlet opening 7 to the outlet opening 8.The piston means divides the space 6 mainly into two parts, the firstpart 6.1 in connection with the inlet opening 7 and the second part 6.2in connection with the outlet opening 8. A spring or the like 10 hasalso been provided in the space 6 for creating a pushing force acting onthe piston means, in a direction opposite the main direction of the fuelflow. A mating face 11 for sealing arrangement has been provided in thepiston means, in the side adjacent the outlet opening 8, andconsequently the body part 5 also comprises the mating face 16 of thesealing arrangement. These allow the piston means to join the body part5 so that the mating surfaces close the fuel flow connection to theinlet opening 7, when the piston means is located in the second partadjacent the part 6.2. Thus, the arrangement according to the inventionalso acts as a flow fuse.

The space 6 and the piston means 9 are cylindrical. The piston means 9comprises a portion 9.2 having a larger diameter, the diameter PD2 ofwhich corresponds with the diameter CD2 of the portion 5.2 of the space.Both the space 6 and the piston means 9 comprise portions 5.1, 9.1, thediameters of which are smaller. The diameter of the portion 9.1 of thepiston means having the smaller diameter is marked with reference PD1.The diameter of the portion 5.1 of the body part having the smallerdiameter is marked with reference CD1.

In the arrangement the piston means 9 and the space 6 are formed so thatwhen the piston means is in the end adjacent the fuel inlet opening 7they delimit at least a third space 6.3, the volume of which depends onthe mutual positions of the piston means 9 and the body part 5. In thiscase, the position of the piston means can also be determined to be atthe end adjacent the first part 6.1 of the space. Firstly, the space 6comprises at least two portions 5.1, 5.2 having two different diametersCD1, CD2, the portion 5.1 having the smaller diameter CD1 being in theend adjacent the part 6.1 of the first space and additionally the pistonmeans 9 correspondingly comprises two portions 9.1, 9.2 having twodifferent diameters PD1, PD2, the portion 9.1 having the smallerdiameter PD1 being located in the end adjacent the first part 6.1 of thespace. Now, the longitudinal length L2 of the smaller portion 9.1 of thepiston means and the longitudinal length L1 of the part 5.1 of space 6having the smaller diameter are both separately shorter than the lengthL3 of the stroke of the piston means 9. Thus, when the portions of thespace 6 and the piston means 9 having the smaller diameter are oneinside the other, a third part 6.3 of the space 6 is formed by theplaces where the diameters change. The piston means 9 and the space 6are cylindrically formed and together they form, by means of theirconstruction and shape, at least two separate sliding surfaces 17, 17′,18, formed at different distances in relation to the central axis of thepiston means and the space. When the piston means retracts from the endadjacent the inlet opening 7 for a certain distance L1 the slidingsurface 17, 17′ ceases to exist and the third part 6.3 of the space andthe first part 6.1 of the space are combined. The effect this has on theoperation of the arrangement is described in the following.

When the piston means 9 is in the initial position, as shown in FIG. 4,the injection is about to start. In this case, the pressure of the fuelis about same in all parts 6.1, 6.2 and 6.3 of the space 6 and the forceof the spring 10 has previously pushed the piston means 9 to the initialposition, i.e. to the end adjacent the inlet opening 7 of the part 6.1of the space. When the injection starts, the injection valve 2 isopened. This causes a pressure decrease in the outlet opening 8 and thesecond part 6.2 of the space 6 connected therewith. As a result of this,the total effect of the forces acting on the piston means is changed andthe piston means starts to retract from the end adjacent the first part6.1 of the space, trying to equalize the pressure difference over thepiston means. This situation is shown in FIG. 5.

The forces mainly determining the movement of the piston means areformed by the pressures prevailing at various parts of the space, andthe force of the spring. In other words, the spring force and the forcedetermined by the pressure in the second part 6.2 of the space and thediameter PD2 of the piston means act against the direction of the fuelflow and the forces acting in the direction opposite these forces arethe force determined by the pressure in the first part 6.1 of the spaceand the diameter DP1 of the piston means and the force determined by thepressure in the third part 6.3 and the difference of the diametersDP2−DP1 of the piston means, in a way known as such. As the injectionproceeds, the piston means continues its movement while the third part6.3 of the space increases and the pressure in this volume tends todecrease. The pressure is however equalized by the fuel flow through theflow channels formed by bores 12, 13. Channel 13 is formed as athrottling channel having a relatively small diameter, and it thusallows controlling the speed of pressure equalization between the thirdpart 6.3 and the first part 6.1 of the space. Generally, the factorshaving an effect on this are flow resistance properties of the flowchannel 12, 13. As the above-mentioned equalization of pressuredifferences slows the movement of the piston means 9, pressure in thesecond part 6.2 of the space 6 as well as in the outlet opening 8 is inthis situation smaller than in the inlet opening 7. Thus, the mass flowof the injected fuel is smaller as well.

The above-mentioned procedure can be illustrated by the equilibriumequation of the forces acting on the piston means.P _(first part 6.1) ·A ₁ +P _(third part 6.3) ·A ₃ =P _(second part 6.2)·A ₂+spring force

With equilibrium in the equation, the pressure p_(third part 6.3) mustdecrease, as the pressure p_(second part 6.2) decreases when theinjection nozzle opens. In this situation the areas remain the same andthe spring force does not change considerably, either. The pressurelevel in the third part 6.3 of the space can be controlled by choosingsuitable diameters for the various portions 5.1, 5.2, 9.1, 9.2 of thepiston means and the space as well as by dimensioning of the flowchannel 12, 13.

In FIG. 6 the piston means has retracted the distance L1 away from theend adjacent the first part 6.1 of the space, and at this distance theportion 9.1 having the smaller diameter exits from the portion 5.1 ofthe space 6 having the smaller diameter. Thus, the sliding surface 17formed by these ceases to exist, whereby the third part 6.3 and thefirst part 6.1 of the space are combined. Subsequent to this thepressure difference between the inlet opening 7 and the outlet opening 8is very small, because the piston means can move without beingessentially dampened.

During normal operation the piston means does not reach the positionshown in FIG. 7. The length of the stroke of the piston means isdetermined by the fuel used during fuel injection. FIG. 7 illustrates asituation, where a malfunction has caused so much fuel to flow throughthe arrangement according to the invention that the piston means 9 is inthe end adjacent the second part 6.2 of the space. Thereby the pistonmeans is joined to the body part 5 so that they together close the flowconnection of fuel between the inlet opening 7 and the outlet opening,i.e. the arrangement according to the invention also acts as a flowfuse.

FIGS. 8–10 show various embodiments of the invention. FIG. 8 illustratesan embodiment in which the portion 5.1 of the space having the smallerdiameter extends inside the space 6 and correspondingly a space has beenarranged in the piston means 9 for accommodating this extension of thebody part. In this embodiment the sliding surfaces 17, 18 are arrangedconcentrically on the same longitudinal position. In this embodiment thethrottling channel 13 is arranged on the body part 5 instead of thepiston means. FIG. 9 shows a construction otherwise corresponding withthat of FIGS. 4–7, but instead of a bore the throttling channel has beenarranged from the plane surface 13″ of the piston means 9. The flowresistance properties of this can be changed by changing the sizethereof and also by arranging the direction of the plane to deviate fromthat of the longitudinal axis, i.e. arranging a slanted plane. Insteadof a plane surface or in addition to it the sliding surface 17 havingthe smaller diameter can be arranged wholly or partially conical (notshown in the figures). FIG. 10 illustrates how the third part 6.3 of thespace 6 is formed by two different parts 6.3, 6.3′. Thus, the portion9.1 of the piston means having the smaller diameter is formed by twodifferent portions 9.1, 9.1′ having different diameters andsimultaneously forming three separate sliding surfaces 18, 17, 17′ withthe body part. Of these, the sliding surfaces 17, 17′ determine theexistence of the parts 6.3, 6.3′ of the space on the basis of thelocation of the piston means. There can naturally be more of these. Inthis embodiment the throttling channels of the separate parts 6.3 andthereby also their dampening properties can be individually determined.

The invention is not limited to the embodiments described here, but anumber of modifications thereof can be conceived of within the scope ofthe appended claims.

1. An arrangement in a fuel injection system for controlling the fuelinjection, the arrangement comprising a body part having a spacearranged therein, through which space the fuel to be injected duringoperation flows, and a fuel inlet opening and an outlet opening openinginto the space, additionally the arrangement further comprises a pistonmeans arranged movably inside the space, the piston means having achannel arranged therein for creating a flow connection between the fuelinlet opening and the outlet opening, whereby in the arrangement thepiston means can divide the space into a first part being in connectionwith the inlet opening and a second part being in connection with theoutlet opening, the arrangement further comprising a spring for creatinga force acting on the piston means in a direction opposite to the maindirection of the fuel flow, wherein in the arrangement the piston meansand the body part delimit at least one third part as the piston means isin the end adjacent the inlet opening or near it, the volume of thethird part being dependent on the mutual positions of the piston meansand the body part.
 2. An arrangement according to claim 1, wherein thepiston means and the space are cylindrically formed and together theyform at least two separate sliding surfaces formed at differentdistances from the central axis of the piston means and the space.
 3. 0narrangement according to claim 1, wherein when the piston means is inthe end adjacent the inlet opening the volume of the third part is atits smallest and as the piston means retracts a certain distance awayfrom the end adjacent the inlet opening the volume of the third partincreases and that as the piston means retracts beyond the certaindistance, the third part and the first part of the space are combined.4. In arrangement according to claim 1, wherein the third part of thespace is in continuous flow connection with the fuel inlet openingand/or the first part of the space.
 5. An arrangement according to claim4, wherein the flow connection is achieved by means of a throttlingchannel.
 6. An arrangement according to claim 1, wherein the space iscylindrical and it comprises at least two portions having differentdiameters, with the portion having the smaller diameter being in the endadjacent the inlet opening and that the piston means correspondinglycomprising two portions having different diameters, with the portionhaving the smaller diameter being in the end adjacent the inlet openingand that both the longitudinal length of the portion of the piston meanshaving the smaller diameter and the longitudinal length of the of theportion of the space having the smaller diameter are shorter than thelength of the stroke of the piston means.
 7. An arrangement according toclaim 1, wherein when the piston means is in the end adjacent the outletopening the piston means joins the body part so that they together closethe flow connection of fuel to the inlet opening.
 8. A fuel injectioncontrol valve comprising: a body part defining an interior space havingan inlet end and an outlet end and through which fuel to be injectedduring operation of the control valve flows, and also defining a fuelinlet opening and a fuel outlet opening that open into the interiorspace at the inlet and outlet ends respectively of the interior space, apiston arranged movably in the interior space and dividing the interiorspace into a first part that is in communication with the fuel inletopening and a second part that is in communication with the fuel outletopening, the piston being formed with a passage for providing a flowconnection between the fuel inlet opening and the fuel outlet opening,and a resilient member urging the piston in a direction opposite to themain direction of the fuel flow, and wherein when the piston is at ornear the inlet end of the interior space, the piston and the body partbound a third part of the interior space, said third part of theinterior space being in throttled communication with the second part forcontrolling equalization of pressure between the second and third parts.9. A fuel injection control valve according to claim 8, wherein thepiston and the interior space are substantially circular in crosssection and have a common central axis, and when the piston is at ornear the inlet end of the interior space, the piston and the body parthave at least two surfaces in sliding contact at different respectiveradial distances from the common central axis of the piston and theinterior space.
 10. A fuel injection control valve according to claim 8,wherein the volume of the third part of the interior space is dependenton the position of the piston relative to the body part, and when thepiston is at the inlet end of the interior space the volume of the thirdpart of the interior space is at a minimum and as the piston moves awayfrom the inlet end the volume of the third part increases.
 11. A fuelinjection control valve according to claim 8, wherein when the pistonmoves away from the inlet end the volume of the third part increasesuntil the piston reaches a predetermined distance away from the inletend, and when the piston means moves beyond said predetermined distance,the third part and the first part of the interior space are combined.12. A fuel injection control valve according to claim 8, wherein thethird part of the interior space is in flow connection with the fuelinlet opening and/or the first part of the interior space.
 13. A fuelinjection control valve according to claim 12, wherein the third part ofthe interior space is in throttled communication with the first part ofthe interior space.
 14. A fuel injection control valve according toclaim 8, wherein the interior space is substantially circular in crosssection and comprises a smaller diameter portion and a larger diameterportion, the smaller diameter portion of the interior space is betweenthe larger diameter portion and the inlet end, the pistoncorrespondingly comprising a smaller diameter portion and a largerdiameter portion, and both the longitudinal length of the smallerdiameter portion of the piston and the longitudinal length of thesmaller diameter portion of the interior space are shorter than thelength of the stroke of the piston means.
 15. A fuel injection controlvalve according to claim 8, wherein when the piston is at the endadjacent the outlet opening, the piston engages the body part so thatthey together prevent flow of fuel from the inlet opening to the outletopening.
 16. A fuel injection control valve according to claim 8,wherein the interior space is substantially circular in cross sectionand comprises a smaller diameter portion and a larger diameter portion,the smaller diameter portion of the interior space is between the largerdiameter portion and the inlet end, the piston correspondinglycomprising a smaller diameter portion and a larger diameter portion, andwhen the piston is at or near the inlet end of the interior space thesmaller diameter portion of the piston is in sliding contact with thebody part bounding the smaller diameter portion of the interior spaceand the larger diameter portion of the piston is in sliding contact withthe body part bounding the larger diameter portion of the interiorspace.